Method of making alpha refractory cast article



" Sept. 20,1932. s UNDER 1,878,879

METHOD OF MAKING A REFRACTORY CAST ARTICLE Filed April 9, 1927 PatentedSept. 20, 1932 UNITED STATES PATENT; OFFICE CYBIL S. LIND'ER, OFCREIGHTON, PENNSYLVANIA, ASSIGNOR 1'0 PITTSBURGH ILATE GLASS COMPANY, ACORPORATION OF PENNSYLVANIA.

METHOD OF MAKING A REFRACTORY CAST ARTICLE Application filed April 9,1927. Serial No. 182,329.

The invention relates to refractory articles, such as tank blocks, andthe like, and the method of making them. The material employed isreferably what is known asmullite, 3Al 2SiO-5, but the invention isapplicable to other refractories, such as chrome ore, or compositionswhich consist only in extent. Hereto ore, cast mullite blocks havebeenmade by fusing adjusted mixtures of alumina and silica, or diasporeand silica, etc. in an electric furnace and then casting the materialinto molds and annealing the castings. This process is relativelyexpensive,\ due to the cost of fusing, and to the requirement of slowand precise annealing. The castings are also relatively fragile andthere is a tendency toward the formation of pipes or holes in the upperportions of the blocks or castings. The present invention is designed toproduce blocks having the same refractory and wearing qualities of theblocks as just described, but at a lower cost, somewhat stronger andfree from blow holes or pipes.

Briefly stated, the process in its preferred form consists in pouringfused mullite into a mold filled, or nearly filled, with crushed or lumpmullite, so that the fused mullite acts as a binder for the lumpmullite, each lump or particle being surrounded by a matrix of the fusedmaterial. The castings as thus produced are duly annealed, preferably ina tunnel vkiln,.as later described, giving a product which is strong andsolid and free from voids. To assist in securing a quick flow of thefused material into all the interst1ces between the solid particles, avibrator .may be employed upon the mold, on the order of those used incompacting molding sand about patterns In sand mold work. It is alsodesirable to preheat the mold and the crushed mullite contentspreliminary to the casting operation, as this promotes the free flow ofthe fused material around the solid particles and tends to improve thebond between the fused and solid material. One apparatus for carryingout the process is shown in the accompan ing drawing, wherein:

The gure is a perspective view of a preheating kiln and leer of thetunnel type, and an electric fusing and casting furnace.

The tunnel kiln, as shown, comprises a preheating section 1, a castingsection 2, and an annealing section 3. A track 4 extends through thekiln, and on this track are mounted a series of cars or trucks 5carrying molds 6. As shown, the molds are open at the top and in fourparts, so that four blocks may be made on each car. Gas burners 7 areemployed for heating the kiln and any desired means may be employed forslowly moving the cars through the kiln. An

opening 8 is provided in the casting section of the kiln, and throughthis opening, the casting occurs from an electric furnace 9, suitablymounted for tilting movement. The opening 8 is closed by a suitablecover after the charge in the furnace is exhausted. In operation, themolds 6 are filled with crushed mullite before entering the kiln. Thesize of the lumps depends on the size of the block to be produced, itbeing possible to use larger lumps in the larger blocks. In a nine inchblock, the lumps preferably run some where near the size of a hickorynut, although the size may be varied, and material may be used in whichthe lumps are of varying sizes. The molds and their contents arepreheated during their passage through section 1, after which the fusedmullite is supplied from the furnace, and the molds carried slowlythrough the annealing and cooling section 3. The casting may also beannealed, if desired, in the molds by covering them with an insulator toretard cooling but the method as above described is preferred.

The method, as above described, involves a considerable degree ofeconomy over the method heretofore used, in which the entire block isformed from the fused mullite. The blocks can be satisfactorily annealedin less than one half the time required by all fused blocks, and nogreat care need be exercised.

Anywhere from to 50 per cent of the block consists of the crushedmullite and this crushed mullite is, pound for pound, much less costlythan the material which makes up the all fused block, since it can bemade in quantity with little requirement for care or precision andwithout annealing. It is also possible to use natural ores, preferablycalcined, as the crushed material, such as kyanite, sillimanite orandalusite, although not so desirable as the artificially fused andcrushed mullite, which is denser and more resistant. The process alsogives an outlet for worn out or cracked, or otherwise defective mul-liteblocks without putting them through the expensive electric fusing operation. Further advantages over the all fused mullite block lie in thefact that the new proces can be conducted with open top molds, whichmakes the casting operation more rapid and convenient, and in the factthat the blocks are freer from pipes and Voids. The term refractory isused in the sense commonly accepted in the ceramic industry; namely, asdescriptive of a material suitable for use in furnaces, and having asoftening point upwards of 3000 degrees F.

What I claim is:

The process of making a refractory cast mullite into lump form,partially filling a mold with the crushed mullite, heating the mold andits content, and then flowing fused mullite into the mold to fill themold, so that the fused mullite surrounds the pieces of crushed mullite.

In testimony whereof, I have hereunto subscribed my name this first dayof April,

CYRE S. LINDER.

